Step 0: The Ingredients

Step 2: Resting & hydrating
This step is not fully necessary, but when mixing by hand or using a lot of whole wheat flour this can definitely help. This phase consists of leaving the dough mix just like that for about 30 minutes.
During this resting period the flour hydrates, more specifically the starch and gluten of the flour are hydrated by water. Water seeps into the grains and will sit around the molecules. If a flour has more fibers and grainy parts (as is the case for coarse whole meal flour for instance), it takes longer for water to travel through. Often a dough is a lot softer and more flexible after resting. It tends to make it easier to knead in the next step.
Step 3: Kneading
There are a lot of recipes out there for breads that don’t require any kneading (what about using a LoafNest?). And it’s true, good breads can be made without any real kneading, although they do tend to require more time and patience. Kneading helps the formation of a light and airy bread. Its main role here is gluten development, gluten are proteins in flour. Kneading stretches the gluten and connects the various gluten molecules with one another. This creates a gluten network

Kneading also introduces air into the dough. These air bubbles are essential for creating an airy bread. Even though yeast will produce gas during rising, it has been found that no new air bubbles are necessarily formed during rising. Instead, existing air bubbles tend to grow. Therefore, creating these air pockets during kneading is vital. It’s these air pockets that allow bread to become fluffy.

Kneading by hand
Kneading by hand requires practice and patience. There are several techniques for doing so, repeatedly smashing the dough on the counter, pulling it apart and many more (watch Great British Bake Off bread baking episodes for great examples. However, personally, I’ve never become good enough at this, resulting in dense breads. A good electric mixer really makes your life a lot easier, saving you time and improving your bread (if your kneading skills aren’t up to scratch just yet).
Electric mixers
The type of mixer suited for your needs mostly depends on the quantities of bread you make. If you’re a home baker with max. 1-2 breads per baking session, I would recommend a regular Kitchenaid stand mixer (it’s what I have) with the dough hook. I wouldn’t recommend buying the mini version, some bread doughs can be pretty tough to knead for the regular mixer already, I don’t think the mini will make it.
One size larger would be the professional version of the Kitchenaid mixer. It isn’t that much larger, but does also have a bit more power. For even larger sizes, we don’t have any personal experience anymore. A common brand of commercial mixers are Hobart mixers, when visiting the Boudin sourdough bakery in San Francisco we saw they used Kemper kneaders. When considering these sizes and up plugs might not work in regular electricity plugs anymore.
Our KitchenAid mixer, our best friend for kneading bread.